扫描透射电镜分析纳米材料的固态稀释效应

Solid state dilution in composition analysis of nano-materials by STEM/EDS

当目标物尺寸小至5 nm后,在EDS成分分析时,样品中被散射的电子束会激发邻近材料的讯号,导致原分析区域内某些特定元素测得的成分浓度远低于目标物原有的浓度,此现象在本研究中称为固态稀释。本研究通过C2光圈改变电子探针尺寸和收敛角度,分析纳米结构元件氮化铟镓多层量子阱在不同试片厚度中铟(In)浓度的变化,借以探讨固态稀释问题。借助STEM仪器操作参数的调整,降低电子束扩展效应,EDS线扫描测得的铟浓度可以提升一倍左右。

When the scale of the object analyzed is smaller than 5 nm,the measured concentration of some specified elements in the interested phase by EDS are much low er than what they should be. The deviation comes from the contribution of signals generated from neighbor phases induced by scattered electrons. The deduction in measured concentration of these specified elements is called solid state dilution in this research. This research studies the problem of solid state dilution by exploring the variation of indium concentration in In Ga N MQWs with different specimen thicknesses as well as the probe sizes and the convergent angles,which are controlled by C2 aperture. The measured In concentration by STEM/EDS can be raised tw ice by changing parameters discussed before.